Family-based gene-by-environment interaction studies: revelations and remedies

Bias can arise in case-control studies of genotype effects if the underlying population is structured (genetically stratified or admixed). Nuclear-family-based studies enjoy robustness against such bias, provided that inference conditions properly on the parents. Investigators have extended family-based methods to study gene-by-environment interactions, regarding such extensions as retaining robustness. We demonstrate via simulations that, if population structure involves the exposure, nuclear-family-based analyses of gene-by-exposure interaction remain vulnerable to inflated Type I error rates through subtle dependencies that investigators have failed to appreciate. Motivated by the Two Sister Study, an ongoing study of families affected by young-onset breast cancer, we consider a design that supplements the case-parents design with a sibling who is not genotyped but provides exposure data. If, in the population at large, inheritance is Mendelian and genotypes do not influence propensity for exposure, then this 4-person (or tetrad) structure permits the study of genetic effects, exposure effects, and genotype-by-exposure interactions. We show for a dichotomous exposure that, when exposure of an unaffected sibling is available, a modification to the analysis of case-sib or tetrad data re-establishes robustness for tests of multiplicative gene-by-environment interaction. We also use simulations to assess the power for detecting interaction across a range of scenarios, designs, and analytic methods.     

Determination of Suitable Imaging Techniques for the Investigation of the Bonding Zones of Asphalt Layers

The material behavior of asphalt depends on its composition of aggregate, bitumen, and air voids. Asphalt pavements consist of multiple layers, making the interaction of the materials at the layer boundary important so that any stresses that occur can be relieved. The material behavior at the layer boundary is not yet understood in detail, as further methods of analysis are lacking in addition to mechanical methods. For this reason, the layer boundary of asphalt structures was analyzed using imaging methods. The aim of this research was to find an imaging method that allows a detailed analysis of the bonding zone of asphalt layers. Two different imaging techniques were used for this purpose. One is a 2-D imaging technique (asphalt petrology) and the other is a 3-D imaging technique (high-resolution computed tomography). Image analysis is a widely used technique in materials science that allows to analyze the material behavior and their composition. In this research, attention was paid to the analysis of the position of the bitumen emulsion, because the contained bitumen is supposed to bond the layers together. It was found that the application of 2-D imaging (asphalt petrology) lacked the precision for a detailed analysis of the individual materials at the layer boundary. With high-resolution computed tomography, a detailed view is possible to visualize the individual materials at the layer boundary in 3D. However, it is difficult to differentiate the materials because there are no gradations in the gray values due to the identical densities. However, it is possible to differentiate between the bitumen from the asphalt and from the emulsion if a high-density tracer is added to the bitumen emulsion for the CT studies. The results of the investigations are presented in this article.     

Gamma oscillations during episodic memory processing provide evidence for functional specialization in the longitudinal axis of the human hippocampus

The question of whether the anterior and posterior hippocampus serve different or complementary functional roles during episodic memory processing has been motivated by noteworthy findings in rodent experiments and from noninvasive studies in humans. Researchers have synthesized these data to postulate several models of functional specialization, However, the issue has not been explored in detail using direct brain recordings. We recently published evidence that theta power increases during episodic memory encoding occur in the posterior hippocampus in humans. In our current investigation we analyzed an expanded data set of 32 epilepsy patients undergoing stereo EEG seizure mapping surgery with electrodes precisely targeted to the anterior and posterior hippocampus simultaneously who performed an episodic memory task. Using a repeated measures design, we looked for an interaction between encoding versus retrieval differences in gamma oscillatory power and anterior versus posterior hippocampal location. Our findings are consistent with a recently articulated model (the HERNET model) favoring posterior hippocampal activation during retrieval related processing. We also tested for encoding versus retrieval differences in the preferred gamma frequency band (high versus low gamma oscillations) motivated by published rodent data.     

SGK1-dependent salt appetite in pregnant mice

Aim: Pregnancy is typically paralleled by substantial increase in maternal extracellular fluid volume, requiring net accumulation of water and NaCl. The positive water and salt balance is accomplished at least in part by increased uptake of salt secondary to enhanced salt appetite. Little is known about the underlying cellular mechanisms. Stimulation of salt appetite by mineralocorticoids, however, is known to be dependent on the serum‐ and glucocorticoid‐inducible kinase SGK1. Methods: To test for a role of SGK1 in the stimulation of salt appetite during pregnancy, fluid intake was recorded in pregnant SGK1 knockout mice (sgk1^?/?) and their wild type littermates (sgk1^+/+). The mice were offered two bottles, one with plain water and the other with isotonic saline. Results: In early pregnancy, i.e. up to 10 days prior to parturition, the sgk1^+/+ mice displayed a significant preference for saline, whereas the sgk1^?/? mice preferred water. Accordingly, the water intake was significantly smaller and saline intake was significantly larger in sgk1^+/+ mice than in sgk1^?/? mice and the preference for water was significantly stronger in sgk1^?/? mice than in sgk1^+/+ mice. Plasma aldosterone levels were higher in sgk1^?/? mice than in sgk1^+/+ mice, a difference contrasting the enhanced salt appetite of sgk1^+/+ mice. Conclusions: SGK1 participates in the stimulation of salt appetite during pregnancy.     

Coffee,ADORA2A,and CYP1A2: the caffeine connection in Parkinson’s disease

Background and purpose: In 1‐methyl‐4‐phenyl 1,2,3,6‐tetrahydropyridine animal models of Parkinson’s disease (PD), caffeine protects neurons by blocking the adenosine receptor A2A (ADORA2A). Caffeine is primarily metabolized by cytochrome P450 1A2 (CYP1A2). Our objective was to examine whether ADORA2A and CYP1A2 polymorphisms are associated with PD risk or modify the caffeine–PD association. Methods: Parkinson’s Epidemiology and Genetic Associations Studies in the United States (PEGASUS) included five population‐based case–control studies. One laboratory genotyped four ADORA2A and three CYP1A2 polymorphisms in 1325 PD cases and 1735 age‐ and sex‐matched controls. Information regarding caffeine (coffee) consumption and other lifestyle factors came from structured in‐person or telephone interviews. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using logistic regression. Results: Two ADORA2A polymorphisms were inversely associated with PD risk – rs71651683, a 5′ variant (adjusted allelic OR = 0.51, 95% CI 0.33–0.80, permutation‐adjusted P = 0.015) and rs5996696, a promoter region variant (adjusted OR for AC and CC genotypes compared with the AA wild‐type genotype were 0.76 (95% CI 0.57–1.02) and 0.37 (95% CI 0.13–1.01), respectively (permutation‐adjusted P for trend = 0.04). CYP1A2 polymorphisms were not associated with PD risk; however, the coffee–PD association was strongest among subjects homozygous for either variant allele rs762551 (P_interaction = 0.05) or rs2470890 (P_interaction = 0.04). Conclusion: In this consortium study, two ADORA2A polymorphisms were inversely associated with PD risk, but there was weak evidence of interaction with coffee consumption. In contrast, the coffee–PD association was strongest among slow metabolizers of caffeine who were homozygous carriers of the CYP1A2 polymorphisms.     

Association of lead exposure with survival in amyotrophic lateral sclerosis

BACKGROUND: Reasons for the variability in survival among ALS cases are unknown but may include exposure to environmental neurotoxicants. OBJECTIVES: We aimed to determine whether lead exposure, assessed by measuring blood and bone lead levels, is associated with survival in amyotrophic lateral sclerosis (ALS). METHODS: We evaluated the relationship of lead exposure to ALS survival in 110 cases from a case-control study conducted in New England in 1993-1996 that included measurements of blood and bone lead. We retrieved information on date and cause of death through 31 December 2003 from the National Death Index Plus and the Social Security Administration Death Index. We evaluated the relationship of survival to lead exposure using Cox proportional hazard analysis, with adjustment for age, sex, and smoking. RESULTS: We found mortality data for 100 of 110 cases; 93 of 100 death certificates mentioned ALS. Median survival from diagnosis to death was 28 months. Shorter survival was associated with older age at diagnosis, female sex, bulbar onset, shorter interval between symptom onset and diagnosis, and reduced lung function. Shorter survival from diagnosis to death had a weak inverse association with blood lead (hazard ratio = 0.9; 95% confidence interval, 0.8-1.0) and a stronger inverse association with patella lead (0.5; 0.2-1.0) and tibia lead (0.3; 0.1-0.7); similar results were found for survival from symptom onset to death. CONCLUSIONS: These results suggest that lead exposure is associated with longer survival in ALS cases and, if confirmed, may shed light on mechanisms involved in disease progression.     

Des-gamma-carboxyprothrombin (PIVKA II) and plasma vitamin K1 in newborns and their mothers.

Assessments of the vitamin K status in newborns and their mothers by means of des-gamma-carboxy-prothrombin (PIVKA II) measurement have given equivocal results. Part of the variability could be attributed to differences in sensitivity (i.e. the ability to detect small concentrations) and validity (i.e. ability to detect vitamin K deficiency) of the methods applied. None of these methods have yet been validated with respect to plasma vitamin K1. In 22 healthy mother/infant pairs PIVKA II was determined using three different assays including ratio Xa/ecarin (Xa/ec), crossed immunoelectrophoresis (CIE), and an ELISA with a monoclonal antibody (MAB). The results were compared with conventional clotting tests and plasma vitamin K1. The following results were obtained: Cord blood: Clotting tests within age-related normal ranges; PIVKA II detection rates: 0/22 (Xa/ec), 1/22 (CIE), 4/22 (MAB); plasma vitamin K1: undetectable in 20/22. Mothers: Clotting tests all within normal range; PIVKA II detection rates: 1/22 (Xa/ec), 0/22 (CIE), 5/22 (MAB); plasma vitamin K1 (pg/ml) for all mothers (median; range): 186; 55-833; for PIVKA II positive mothers: 213; 59-699. PIVKA II detectability in newborns and mothers was not correlated. The results show an increase in sensitivity for PIVKA II detection in the order of MAB > CIE > Xa/ec. Due to the very low plasma vitamin K1 at birth, no correlation was possible between cord PIVKA II detectability and plasma vitamin K1. However, in mothers at term PIVKA II MAB appears to be unrelated to the vitamin K status.     

Mercuric ions are potent noncompetitive antagonists of human brain kainate receptors expressed in Xenopus oocytes

Kainate receptors are one of the major subtypes of excitatory amino acid receptors in the vertebrate central nervous system. Using Xenopus oocytes injected with RNA from human temporal cortex, it is possible to detect electrophysiologically the expression of this receptor subtype in these cells. Ions of the group IIb elements, particularly mercuric ions, are highly potent, noncompetitive inhibitors of these human brain kainate receptors. Mercury-containing sulfhydryl reagents are also very effective, irreversible blockers of the kainate-gated currents of these oocytes. The recovery of kainate-activated currents after washout of Hg2+ is slow and incomplete relative to that seen after treatment either with Cd2+ or Zn2+. Cysteine or dithiothreitol can accelerate this recovery of kainate-inducible currents after Hg2+ inhibition. Besides the toxicological implications of these results, mercury compounds may be useful for future studies of the structure and physiology of the kainate receptor-channel complex.